There are many articles appeared on the attempted specific targeting of pathogenic cells, in particular, cancer cells utilizing cytotoxic drug conjugated to cell-surface receptor binding agents, such as antibodies (Sela et al, in Immunoconjugates 189-216 (C. Vogel, ed. 1987); Ghose et al, in Targeted Drugs 1-22 (E. Goldberg, ed. 1983); Diener et al, in Antibody mediated delivery systems 1-23 (J. Rodwell, ed. 1988); Silverstein, Nat. Immunol. 2004, 5, 1211-7; Fanning et al, Clin. Immunol. Immunopathol. 1996, 79, 1-14; Ricart A. D., et al., Nature Clinical Practice Oncology 2007, 4, 245-255; Singh R. et Rickson H. K., Therapeutic Antibodies: Methods and Protocols, 2009, 525, 445-467), folic acids (Sudimack, J. et al, Adv. Drug Delivery Rev. 2000, 41, 147-162; Reddy, et al, Mol. Pharm. 2009, 6, 1518-25); PMSA (prostate specific membrane antigen) binding ligands (Low, et al, WO 2009/026177 A1); albumin with peptides (Temming, et al, Bioconjugate Chem. 2006, 17, 1385-1394); cobalamin and proteins (Gupta, et al, Crit. Rev. Therap. Drug Carrier Syst. 2008, 25, 347-79; Petrus, et al, Angew. Chem. Int. Ed. 2009, 48, 1022-8); carbohydrate (Darbre, et al, Curr. Top. Med. Chem. 2008, 8, 1286-93); bioactive polymers (Dhar, et al, Proc. Natl. Acad. Sci. 2008, 105, 17356-61); dendrimers (Lee, et al, Nat. Biotechnol. 2005, 23, 1517-26; Almutairi, et al; Proc. Natl. Acad. Sci. 2009, 106, 685-90); nanoparticles with binding ligands (Liong, et al, ACS Nano, 2008, 19, 1309-12; Medarova, et al, Nat. Med. 2007, 13, 372-7; Javier, et al, Bioconjugate Chem. 2008, 19, 1309-12); liposomes (Medinai, et al, Curr. Phar. Des. 2004, 10, 2981-9); viral capsides (Flenniken, et al, Viruses Nanotechnol. 2009, 327, 71-93), etc.
Different families of cytotoxic agents like calicheamicin derivative (Giles, et al Cancer 2003, 98, 2095-104; Hamann, et al, Bioconjug Chem 2002, 13, 47-58), maytansin derivative (Widdison, et al, J Med Chem 2006, 49, 4392-408; Ikeda, et al, Clin Cancer Res 2009, 15, 4028-37; Xie, et al, Expert Opin Biol Ther 2006, 6, 281-91), auristatins (Sutherland, et al, J Biol Chem 2006, 281, 10540-7; Doronina, et al, Bioconjug Chem 2006, 17, 114-24), taxane derivatives (Miller, et al, J Med Chem 2004, 47, 4802-5; WO 06061258), leptomycine derivatives (WO 07144709), CC-1065 and analogues (Suzawa, et al, J Control Release 2002, 79, 229-42; Suzawa, et al, Bioorg Med Chem 2000, 8, 2175-84; WO 2007102069), doxorubicin (Trail, et al, Science 1993, 261, 212-5; Saleh et al, J Clin Oncol 2000, 18, 2282-92), daunorubicin, vincristine, vinblastine, mitomycin C, or chlorambucil have been used for the conjugation with a cell-surface receptor binding agent, in particular with antibodies (Wu, et al, Nat. Biotechnol. 2005, 23, 1137-1146. Ricart, et al, Nat. Clin. Pract. Oncol. 2007, 4, 245-255).
The use of a cell-surface receptor binding agent, particularly a targeting antibody having an affinity for the pathogenic cells makes it possible to deliver the cytotoxic agent directly in the vicinity or directly in the pathogenic cell, thus increasing the efficiency of the cytotoxic agent while minimizing the side-effects commonly associated with the cytotoxic agents.
Several short peptidic compounds that found to have biological activity have been isolated from natural sources. One of them, Tubulysins (structures shown below), which were original isolated by Hofle and Reichenbach et al. (GBF Braunschweig) from a culture growth of the
 TubulysinRiRiiRiiiACH2OCOCH2CH(CH3)2OCOCH3OHBCH2OCOCH2CH2CH3OCOCH3OHCCH2OCOCH2CH3OCOCH3OHDCH2OCOCH2CH(CH3)2OCOCH3HECH2OCOCH2CH2CH3OCOCH3HFCH2OCOCH2CH3OCOCH3HGCH2OCOCH═CH2 OCOCH3OHHCH2OCOCH3OCOCH3HICH2OCOCH3OCOCH3OHUHOCOCH3HVHOHHZHOHOHPretubulysinCH3HH(The structures of existing tubulysin compounds)myxobacterial strains of Archangium gephyra (F. Sasse et al. J. Antibiot. 2000, 53, 879-885; WO9813375), are members of group of antimitotic peptides that inhibit tubulin polymerization in dividing cells, and thus inducing apoptosis. With the exceptional potency exceeding that of vinblastine, taxol and epothilones (Wipf, et al, Org. Lett. 2004, 6, 4057-60; Peltier, et al, J. Am. Chem. Soc. 2006, 128, 16018-9; Wipf, et al, Org. Lett., 2007, 9, 1605-1607; Wang, et al, Chem. Biol. Drug Des. 2007, 70, 75-86; Pando, et al, Org. Lett. 2009, 11, 5567-9), these antimitotic peptides are exciting leads for targeted therapies. Structurally, the tetrapeptide tubulysins comprise of N-methylpipecolinic acid (Mep) at the N-terminus, isoleucine (Ile) as the second residue, the unique thiazole-containing tubuvaline (Tuv) as the third residue, and two possible γ-amino acids at the C-terminus (tubutyrosine (Tut) or tubuphenylalanine (Tup)). Despite several tubulysins have recently been synthesized, significant general toxicities (>15% animal body weight loss) of the existing tubulysins at doses required for achieving a therapeutic effect compromise their efficacy (US Patent appl. 2010/0048490). We have been interested in the art of a conjugate of a cell surface binding ligand, particularly using an antibody to conjugate with tubulysin derivatives for having significantly lower general toxicity, yet useful therapeutic efficiency. However, the tubulysins are hardly soluble in a buffer solution, resulting in significant amount of antibody aggregation when conjugated with the tubulysins. A simpler analog, such as using phenyl alanine (Phe) and tyrosine (Tyr) to replace Tup and Tut components respectively for the antibody conjugation leads to the hydrolysis of Phe and Tyr in the animal blood circulation and generates the much less potent Mep-Ile-Tuv moiety (over 200 fold less potency than tubulysin A and D). Here this patent discloses conjugates of a cell surface binding ligand with water soluble and stable, as well as in lower systematical toxicity, tubulysin derivatives and using these conjugates for treating cancer and immune disorders.